Recent years have seen development of biometric authentication techniques for judging whether or not to authenticate an individual using biometric information such as a fingerprint or a hand vein pattern. Biometric authentication techniques are widely used, from large-scale systems with a number of registered users, such as access control systems, border control systems, or national identification number systems, to apparatuses used by specific individuals, such as computers or mobile terminals.
For example, in order to use a hand vein pattern as biometric information, a biometric authentication apparatus acquires a biometric image representing the vein pattern as an input biometric image. Then, the biometric authentication apparatus matches the input biometric information that is the vein pattern of a user represented in the input biometric image with registered biometric information that is a hand vein pattern represented in a biometric image of a registered user registered in advance. The biometric authentication apparatus authenticates the user as the registered user having proper authority when it judges that the input biometric information matches with the registered biometric information based on a result of the matching process. Additionally, the biometric authentication apparatus allows the user to use an apparatus incorporating the biometric authentication apparatus or another apparatus connected with the biometric authentication apparatus.
When a user registers biometric information in the biometric authentication apparatus (hereinafter referred to simply as “at the time of registration”), a posture of a body part including the biometric information is preferably the same as a posture of the body part when matching biometric information of the user and biometric information of a registered user is performed (hereinafter referred to simply as “at the time of matching”). The use of the same posture at the time of matching and at the time of registration increases a degree of similarity between a shape of biometric information captured in a biometric image obtained at the time of registration and a shape of biometric information captured in a biometric image obtained at the time of matching. As a result, a genuine acceptance rate is improved. However, practically, even when the registered user himself or herself requests authentication as a user, the posture of the body part including biometric information at the time of registration sometimes differs from the posture of the body part at the time of matching. Accordingly, the shape of biometric information captured in a biometric image obtained at the time of registration does not completely match with the shape of biometric information captured in a biometric image obtained at the time of matching.
Thus, techniques have been proposed for performing matching process by correcting or considering a difference between the shape of biometric information in an image at the time of registration and the shape of biometric information in an image at the time of matching due to a difference in posture (for example, see Japanese Laid-open Patent Publication No. 2002-117405 or Japanese Laid-open Patent Publication No. 2010-15365).
For example, Japanese Laid-open Patent Publication No. 2002-117405 discloses a palm-shape authentication method for matching a palm-shape image and a registered palm-shape image by detecting a rotation angle of a hand from palm-shape image data and correcting a positional deviation from a rotation angle of a registered hand in a registered palm-shape image registered in advance by detecting a palm-shape of a user.
In addition, Japanese Laid-open Patent Publication No. 2010-15365 discloses a biometric authentication apparatus that performs authentication by comparing at least a vein pattern image of a subject and a template of the subject based on evaluation results on a relative position between a skin surface pattern image of the subject and the template thereof.